Charles A. Bowsher, the comptroller general, said extending the fund's borrowing ability was an unrealistic to handle the growing crisis that would "ultimately hurt the administration's credibility."

"I've been through taxpayer bailouts before, and this is how they often get started," Mr. Bowsher said Friday, referring to the savings and loan bailout. He is highly regarded on Capitol Hill for his nonpartisan and intense scrutiny of bank regulators and other government agencies. His opinion could become a serious obstacle to passage of the plan.

Officials have predicted that the $8.4 billion insurance fund will be insolvent in the next year or two. The fund is at its lowest level in relation to deposits in its 57-year history.

Fears of a taxpayer bailout of the bank fund were heightened Thursday by the surprise disclosure by L. William Seidman, chairman of Federal Deposit Insurance Corp., that the administration was actually seeking $70 billion in borrowing authority, not the $25 billion it had said earlier in the week.

Mr. Bowsher heads the General Accounting Office, the agency thataudits and investigates government programs for Congress. He said the GAO would be issuing its recommendations to Congress for reorganizing the bank insurance fund within the next few weeks.

The agency has been sharply critical of regulators for failing to take prompt action that could have avoided the failures of many banks.

Mr. Bowsher said Congress would be "foolish" to increase the borrowing authority of the FDIC, instead of simply providing adequate funds and quantifying the actual losses.

The Treasury plan, presented as an effort to avert the use of taxpayer funds, provides for a $25 billion credit line with the Federal Reserve and another $45 billion from the Federal Financing Bank.